When to Deploy

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I've searched the documentation, but haven't been able to find an answer to this question.  In general, when are the flaps lowered to various levels, and when are the gear lowered?  How is it done in the real aircraft?

I've tried methods based on altitude, or distance from the runway, or speed, but I'm not convinced I'm doing it right.  My impression from the tutorial is that 1 degree is lowered when the aircraft decelerates to around 200 knots, and then successively lowered each time the target speed is reached for that flap setting until the landing flap setting is achieved.  Is this correct?  

I live near an airport, and I've noticed that the airliners drop their gear about 5 miles from the runway at an altitude of about 2500 feet. Seems like in the sim I'm lowering gear and flaps at a much greater distance, and then flying slowly to the runway.

I have the same questions for the 747 and 777, so if anyone wants to comment on differences in technique between these aircraft I'm interested in hearing your thoughts.

I've been flight simming since the 1980's, and these PMDG aircraft are far and away the most interesting and challenging I've seen.

Thanks in advance.



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good question. Usually i do it based on my own judgement and what I need. But yeah, gear down when established e.g. And that also means in the 737 putting down flaps 15. Until 10 dme and then going down to 160 knts > landing config while depending the glideslope. But I also know I do it wrong

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If you follow the FCOM normal procedures does it not give a basic configuration sequence during the approach? 

Flap extension is based on airspeed - in all (I think) of Boeing's jets the schedule is based on Vref. So you calculate your Vref, then you add increments of 20 knots for the flap speeds. In the 767 - because that's the last time I had to do it manually! - 

Vref +100 = minimum clean

Vref +80 = flap 1 minimum manoeuvre speed

Vref +60 = Flap 5 minimum manoeuvre speed

Vref +40 = Flap 15 minimum manoeuvre speed

Vref +20= Flap 20 minimum manoeuvre speed

The 737/747 speedtape flap speeds are based on exactly the same principle (make sure the correct Vref is entered in the Approach Ref page or he speeds will be wrong). The basic idea is that you must not decelerate below the manoeuvre speed for the configuration without selecting the next stage of flap (so you must not decelerate below flap 5 manoeuvre speed until you have selected flap 15).

Note that on departure this is slightly different on that because you are accelerating you retract to the next step as you go through the manoeuvre speed for the current configuration (eg at flap 5 manoeuvre speed select flap 1).

Gear down is usually coincident with or just after flap 20 selection but check the books (IIRC the 737 will give you a gear warning if you go beyond F15 without gear). In the interest of noise abatement and fuel efficiency it is usually preferable to delay gear extension slightly. The 747 will happily go down a 3 degree ILS with F10, gear up, idle thrust and 160-180kt which is nice and quiet! 

Your bottom line for gear extension is that you must comply with the stable approach criteria, which generally means you must be fully stable and in the landing configuration with the landing checklist complete by 1000R. In the 747 I would want the gear selected down by 1500R at the very latest otherwise you will struggle to get slowed down and configured in time.

Don't forget also that the gear is an excellent source of drag and therefore taking the gear early/out of the normal sequence with the flaps is an excellent way to get slowed down if you are a little high/fast (but once the gear is down it is down - don't go retracting it again!)

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My normal approach flow is F5 on base or vector to intercept final course (fly the bugged speed discussed by Simon), approaching final descent or GS F15 and gear down on GS intercept and F30 about 1800 ft AGL.  I always use F30 in the NGX unless I have a short landing.  This is a pretty simple flow and works in most cases.

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Just to add a little further: in real life, gear down/landing flap at glideslope intercept would generally be considered a pretty conservative profile in real airline ops. Most operators will tend to fly "decelerated" (low drag/noise) approaches to save on fuel and reduce noise.

At busy airfields it is typical to be speed-restricted by ATC to within a few miles out (160 to 4 DME, 170 to 5, 180 to 6 are typical), so at this point the aim is to maintain the assigned speed with as little drag (and therefore as little thrust) as possible. In the 744, as I say, F10/F20 (depending on weight) and gear up will generally give you a nice descent on the glide with close to idle thrust and 160 kt.

Gear extension can then come at around the time when you want to reduce to final approach speed (i.e. Vref + increment) as the extra drag will help you slow down. 160 to 4 can be a little challenging in a slippery aeroplane if you want to make the stable approach criteria at 1000R, especially if there is any tailwind around; the usual technique is to select the speed to Ref + increment at about D4.5, gear down immediately after selecting the speed down (don't do the gear first as the extra drag will cause the A/T to add thrust to maintain speed!) and then get the flap out on schedule. If particularly light/tailwind etc you may need to get the drag on earlier if you are going to get landing flap down by 1000R.

One other point I forgot to make: don't use the flaps as speedbrakes! What I mean by this is: don't be tempted to extend flap at the upper end of the speed range (e.g. selecting F20 at Ref + 55) in order to slow the aeroplane down with the extra drag: the flaps are not designed for this purpose and you will be putting unnecessary stress on them. If you need drag, use the gear and/or speedbrake (note that some aircraft have restrictions on the use of speedbrake with flap extended: check the FCOM). In an ideal world you want a smooth deceleration, selecting the next stage of flap perhaps 5 knots or so above the manoeuvre speed so that you can then wind the speed down further and avoid the thrust levers coming forward (as mentioned: you shouldn't be bugging a speed below the manoeuvre speed for the current configuration).

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